Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
rb_insert_pages. x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).
No functional change intended.
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Masami Hiramatsu <mhira...@kernel.org>
Signed-off-by: Uros Bizjak <ubiz...@gmail.com>
---
kernel/trace/ring_buffer.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a1651edc48d5..3e2a6478425c 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2048,7 +2048,7 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
retries = 10;
success = false;
while (retries--) {
- struct list_head *head_page, *prev_page, *r;
+ struct list_head *head_page, *prev_page;
struct list_head *last_page, *first_page;
struct list_head *head_page_with_bit;
struct buffer_page *hpage = rb_set_head_page(cpu_buffer);
@@ -2067,9 +2067,9 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
last_page->next = head_page_with_bit;
first_page->prev = prev_page;
- r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
-
- if (r == head_page_with_bit) {
+ /* caution: head_page_with_bit gets updated on cmpxchg failure
*/
+ if (try_cmpxchg(&prev_page->next,
+ &head_page_with_bit, first_page)) {
/*
* yay, we replaced the page pointer to our new list,
* now, we just have to update to head page's prev
--
2.41.0
